1. Field of the Invention
The present invention relates to a tape cassette for housing a thin-metal-film magnetic tape suitable for magnetic recording at high densities.
2. Description of the Prior Art
The modern magnetic recording technology, which is based on flux differentiation principles, has been developed together with the continued advance of magnetic tape/head systems as signal transducers.
Higher recording densities are essential for more advanced magnetic recording. To achieve magnetic recording at higher densities, efforts have been made to develop metal tapes which are to replace conventional ferric oxide tapes.
A thin-metal-film magnetic tape includes a Co-Ni-O layer deposited as a magnetic recording layer on a high-polymer film by oblique evaporation. Such a magnetic tape is known as an ME (Metal-Evaporated) tape, and is being used as a 8-mm video tape for higher recording densities.
The thin-metal-film magnetic tape is also expected to be effective in high-density digital recording. There have been made attempts to achieve better solutions to various problems caused by shorter wavelengths of signals to be recorded and also problems inherent in the materials of the thin-metal-film magnetic tape.
Particularly, a tribological approach to the problems is to give more durability to the magnetic recording layer which is made smooth to minimize spacing loss that presents a serious drawback to shorter-wavelength signals. In addition, efforts have also been made to maintain a total number of magnetic fluxes while improving shorter-wavelength characteristics with thinner magnetic recording layers, and also to prevent aging-induced deterioration due to corrosion.
Various proposals which have been put forward for the solution of the above problems basically fall under the following schemes (1) through (5):
(1) Small protrusions are provided on a magnetic recording layer to improve tape friction and abrasion (see, for example, IEEE TRANSACTIONS ON MAGNETICS, Vol. MAG-21, No. 5, pages 1524.about.1526 (1985), Japanese Laid-Open Patent Publications Nos. 59-207422 and 61-284829).
(2) A partially oxidized layer is effectively utilized in order to improve corrosion resistance and abrasion resistance, without having a magnetic metal film exposed (see, for example, Japanese Patent Publication No. 57-29770 and Japanese Laid-Open Patent Publication No. 61-153856).
(3) The materials and structure of a magnetic recording layer are arranged for higher resistance to corrosion and abrasion (see, for example, Japanese Laid-Open Patent Publications Nos. 59-119532 and 61-139920).
(4) Direct sliding contact between a magnetic recording layer and a magnetic head is avoided, and a protective lubricating layer is provided for the essential functioning of the magnetic layer and durability against wear due to sliding movement (see, for example, Japanese Laid-Open Patent Publications Nos. 60-93635, 61-131231, 61-142525, 61-151830, 61-242323, 61-250825, 61-280019, 62-8325, and Japanese Patent Publication No. 61-61444).
(5) Combinations of the above proposals.
The magnetic tapes which have been improved as described above are generally housed in tape cassettes.
Most of the presently available tape cassettes are composed of components molded of synthetic resin and assembled together. Materials, designs, structures for easy assembly, mechanical properties, and weather resistance capabilities for tape cassettes are selected and improved according to various existing standards. For recent high-density recording applications, tape cassettes are hermetically sealed in order to prevent entry of foreign matter for protection against dropouts and head clogging (see, for example, Japanese Utility Model Publication No. 57-9983, Japanese Laid-Open Utility Model Publications Nos. 58-190875, 61-48481, 61-118175, and Japanese Laid-Open Patent Publication No. 61-5487).
Tape cassettes which are well hermetically sealed, including commercially available 8-mm video tape cassettes, R-DAT tape cassettes, and M-11 format tape cassettes for broadcasting use, are preferable in terms of improved weather resistance of thin-metal-film magnetic tapes housed therein. These hermetically sealed tape cassettes are helpful in allowing thin-metal-film magnetic tapes to be improved for practical application.
Recent widespread use by consumers and industries of video cassette recorders and video cameras has expanded their applications to a greater variety of subjects or images to be recorded under various conditions. It has been required for these video devices to withstand more rigorous environmental conditions such as high temperatures, high humidities, low humidities, and corrosive gas atmospheres in the presence of H.sub.2 S, SO.sub.2, Cl.sub.2, NO.sub.x, and other harmful gases.
Conventional tape cassettes which would not cause any problems when used under normal conditions may often give rise to dropouts and head clogging during use, even for a short period of time, in harsher environments containing high concentrations of the above gases.